Catalytic pressureless oiling

The catalytic pressureless oiling ( CO ) or thermoplastic low temperature catalytic conversion ( NTK ) is a technical depolymerization . Artificial or natural polymers and long-chain hydrocarbons are converted into shorter-chain aliphatic hydrocarbons, comparable to synthetic light oil ( diesel fuel ), with the addition of a zeolitic catalyst at temperatures below 400 ° C without excess pressure . The efficiency is very dependent on the raw material and is between 30% (for biomass) and up to 90% (for high-energy plastics and oils).

The main area of application is the conversion of waste into fuel (synthetic diesel; i.e. neither biodiesel nor mineral diesel). The technology is currently still in development; pilot plants have been in operation in Mexico since 2004 and in Canada since 2007 .

The light oils produced according to the NTK / KDV process are to be classified as second-generation alternative fuels , provided biomass is processed as a starting material.

The KDV procedure at a glance

Source material (input)

All high-energy substances that contain hydrocarbons are used as the starting material.

Industrial recyclables and residues: for example used oils and grease residues, rubber tires , plastic material (including PVC ), sorted waste (including hospital waste), sewage sludge
Biogenic residues and renewable biological raw materials: Plant residues such as almond shells , rapeseed (the entire plant), wood , straw , animal waste

Before the reaction, the starting material must be shredded and have a small grain size (<1 mm). Metals, stones and other impurities must be removed. In addition, the starting material must be dry or dried, as otherwise water vapor will develop spontaneously when it is introduced into the hot oil. The energy required for drying and grinding reduces the energy balance of the process.

Additives

As catalyst are zeolites of the pentasil type and Wassalith used. The required amount of catalyst is approx. 1–6% of the input, depending on the respective input material. If the starting material contains chlorine and fluorine, hydrated lime is used to neutralize the acids produced during the process. In addition, high-boiling thermal oil is used to mediate reactions and to seal off air.

The catalyst and neutralizer are common, commercially available, chemically unproblematic products. The catalyst is relatively expensive.

Reaction principle

The highly concentrated mineral catalyst causes a conversion of the input materials under technically controllable conditions at high temperatures and in the absence of air in hot oil.

In the reaction vessel (separator), the dry, heavily comminuted raw material (input) and the catalyst are mixed in hot thermal oil and heated to up to 400 ° C. At these temperatures the starting material loses its solid consistency and liquefies. Most plastics melt and emulsify in thermal oil. The added catalyst cracks the hydrocarbons .

The short-chain hydrocarbons that are formed evaporate from the hot oil mixture at boiling temperatures of less than 340 ° C. In a subsequent distillation column , they are obtained from the steam as a mixture of aliphatic hydrocarbons (of type C10-C22). This mixture has the properties of conventional diesel fuel .

If the input mass contains sulfur compounds, these must be removed further. Halogens, e.g. B. in PVC or other plastics are bound by the neutralizer to form salts. The hydrocarbons not cracked during the reaction and the other substances present in the input material, such as B. metals, salts, carbon, lignins (in wood), but also used and decomposed catalyst remain in the reaction vessel and are discharged by means of a screw. The mixture of used catalyst and other residues and oils must be processed further and disposed of.

Due to the temperatures of less than 400 ° C (in contrast to pyrolysis), no highly toxic dioxins or furans are formed from halogen-containing plastics, as these only arise at higher temperatures. The catalyst and temperatures of more than 250 ° C should destroy all bacteria, viruses and prions during the reaction , but recent research in the field of prions has shown resistance even at temperatures above 400 ° C.

End products (output)

distillation

The distillation process separates the following products:

volatile, flammable hydrocarbons , ( aromatics ) and gases
a middle distillate, as a mixture of short-chain aliphatic hydrocarbons
Water, as process water (due to excess oxygen that binds hydrogen)
small amounts of CO ₂ and CO through the reaction of the carbon contained in them with organically bound oxygen
Nitrogen and ammonia in the processing of animal, protein-containing products

When organic substances are oiled, CO _{2 is} split off in the KDV system , and N _{2 is also produced} . CO and ammonia are not generated in the low-temperature operation with turbines.

Residues

The following substances remain in the reaction vessel after the process:

Used catalyst
Salts from the reaction of the neutralizer with halogens
Mineral components of the input material
Metals and metal salts, if present in the input material, etc. a. Heavy metal salts from dyes and plastics
carbon

The residues of the reaction, such as the formed salts, heavy metals and inorganic ash components (glass, metal, ceramic) are separated in a special heating chamber . The hydrocarbons come back into the system as a gas from the heating chamber and the inorganic substances are separated from the heating chamber via a discharge system.

Differentiation from pyrolysis

The catalytic pressureless oiling is to be differentiated from the pyrolysis as follows: In the pyrolytic process at temperatures of 450 to 1200 ° C extensive cracking of the CC bonds occurs and cyclizations to aromatics with partial formation of polycyclic aromatic hydrocarbons (PAH) with toxic properties. In the thermocatalytic implementation of z. B. organic matter distill aliphatic hydrocarbons (crude oils) at boiling point from the catalytic reactor. What remains are activated carbon and mineral salts.

Development of the process

Fundamental research on the chemical reaction of the process was carried out in the 1980s by Ernst Bayer at the University of Tübingen and was first patented worldwide in 1981. The process known by Bayer as NTK (low pressure thermal conversion) and the catalysts used are now state of the art.